The present invention relates to an apparatus for printing upon a document. In particular it relates to an apparatus including a print wheel and a hammer, the hammer being operative to urge the document against an ink ribbon and in turn for the ink ribbon to contact the print wheel and leave a record of a selected character upon the document.
The present invention is hereinafter described with reference to use in a document encoding machine. It is to be appreciated that the invention is not restricted to such use and can be used in numerous other types of apparatus where printing is required.
In a document encoding machine checks and other documents have data automatically read therefrom, have machine readable data printed thereon, and are processed such that amounts and/or quantities are automatically recorded. The checks and documents are passed from an input stack or pocket, through various processing stages, and are placed in or distributed among one or more output stacks or pockets.
The characters printed upon a check or other document are required to be machine readable at a later stage either by means of a magnetic reading device employed to read characters printed in magnetic ink or by means of an optical reading device which detects the visible outline of the printed characters and converts them to machine interpreted code.
It is to be appreciated that, in order for the automatic process of reading to be effective, printing must be as free of extraneous marks and blemishes as possible.
The present invention seeks to provide an impact printer capable of achieving the aim of blemish-free printing at low cost. The present invention seeks to achieve that aim without use of complex or precision parts.
In the prior art an impact printer was provided with a rotary print wheel. An ink ribbon was provided adjacent to a predetermined face of the print wheel. The print wheel would be turned about its axis of rotation until a selected character was adjacent to the ink ribbon. A hammer would move in a predetermined direction to strike a document towards the ink ribbon. The ink ribbon and document would together strike the print wheel and a visible record would be obtained. Because of the risk of the document inadvertently rubbing against the ink ribbon and leaving an extraneous mark or blemish, a ribbon shield was provided attached to a housing for the print wheel. The ink ribbon was passed about the leading edge of the housing between the print wheel and the document position. The shield was made from thin brass sheet and was rigid. Clearances were critical and the whole assembly could be damaged and require replacement and expensive setup should any mis-strike of the hammer cause damage or mere attrition or abrasion rub away the shield through extended use.